Deep optical imaging of the gamma-ray pulsar J1048-5832 with the VLT

TL;DR

Deep optical observations of gamma-ray pulsar J1048-5832 with the VLT set upper limits on its optical brightness, revealing its faintness and inefficiency in optical and X-ray emissions, and identified a potential nebula counterpart.

Contribution

This study provides the deepest optical limits for J1048-5832 and compares its multi-wavelength properties with other pulsars, highlighting its optical-X-ray inefficiency and potential nebula features.

Findings

No optical detection of the pulsar, with upper limits of V > 28.4 mag and R > 28.1 mag.

Estimated interstellar extinction of 2 mag consistent with X-ray absorption.

Identified a candidate optical counterpart in the pulsar nebula region.

Abstract

(abridged) PSR J1048-5832 is a young Vela-like pulsar that was recently detected in gamma-rays with Fermi, and also in X-rays with Chandra and XMM-Newton. It powers a compact PWN visible in X-rays. We present deep optical observations with the ESO Very Large Telescope to search for optical counterparts of the pulsar and its nebula and to explore their multi-wavelength emission properties. The data were obtained in V and R bands and compared with archival data in other spectral domains. We do not detect the pulsar in the optical and derive informative upper limits of R > 28.1 mag and V > 28.4 mag for its brightness. Using a red-clump star method, we estimate an interstellar extinction towards the pulsar of 2 mag, which is consistent with the absorbing column density derived form X-rays. The respective distance agrees with the dispersion measure distance. We reanalyse the Chandra X-ray data and compare the dereddened upper limits with the unabsorbed X-ray spectrum of the pulsar. We find that regarding its optical-X-ray spectral properties this gamma-ray pulsar is not distinct from other pulsars detected in both ranges. However, like the Vela pulsar, it is very inefficient in the optical and X-rays. Among a dozen optical sources overlapping with the pulsar X-ray nebula we find one with V = 26.9 and R = 26.3 mag, whose colour is slightly bluer then that of the field stars and consistent with the peculiar colours typical for pulsar nebula features. It positionally coincides with a relatively bright feature of the pulsar X-ray nebula, resembling the Crab wisp and locating in 2 arcsec from the pulsar. We suggest this source as a counterpart candidate to the feature. Based on the substantial interstellar extinction towards the pulsar and its optical inefficiency, further optical studies should be carried out at longer wavelengths.